Radiative relaxation in isolated large carbon clusters: Vibrational emission versus recurrent fluorescence.

Recurrent fluorescence (RF) from isolated carbon clusters containing between 24 and 60 atoms is theoretically investigated as a function of internal energy, cluster size, and structural features. The vibrational relaxation kinetics and the associated IR emission spectra are determined by means of a Monte Carlo approach with vibrational density of states computed in the harmonic approximation. RF is generally found to be highly competitive with vibrational emission. The behaviors predicted for clusters of various sizes and archetypal structures indicate that the IR emission spectra are strongly influenced by RF, an energy gap law being obtained for the evolution of the RF rate constant depending on the electronic excitation state. The present results are relevant to the photophysics of the interstellar medium and could contribute to elucidating the carriers of the extended red emission bands and the continuum emission lying below the aromatic infrared bands believed to originate from mixed aromatic-aliphatic compounds.

Atomistic modeling of the infrared response of fullerenes under hydrostatic pressure.

The anharmonic infrared spectrum of individual C60 and C70 fullerenes under hydrostatic pressure was theoretically computed by means of atomistic simulations. Using a tight-binding model for the fullerenes and a simple particle-based pressure-transmitting fluid, the structural and vibrational properties were determined at room temperature and up to 20 GPa. All properties generally exhibit relative variations that are linear with increasing pressure, but whose magnitude can be comparable to pure thermal effects. The bond length contraction usually agrees with existing results, and for C70 our approach manages to reproduce the occasionally negative pressure coefficient found for some low-frequency modes in experiments.

Synchrotron-based valence shell photoionization of CH radical.

We report the first experimental observations of X(+) (1)Σ(+)←X (2)Π and a(+) (3)Π←X (2)Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg states of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes.

Low-energy vibrational spectra of flexible diphenyl molecules: biphenyl, diphenylmethane, bibenzyl and 2-, 3- and 4-phenyltoluene.

Gas phase absorption far-infrared (FIR) spectra of six flexible hydrocarbon molecules containing two phenyl groups -biphenyl, diphenylmethane, bibenzyl and 2-, 3-, 4-phenyltoluene- are reported for the first time, allowing an accurate determination of most of their active low-frequency vibrational modes. DFT calculations have been carried out at the harmonic and perturbative anharmonic levels to predict the vibrational spectra of these molecules and unambiguously assign observed vibrational modes.

Atomistic modeling of vibrational action spectra in polyatomic molecules: nuclear quantum effects.

The response of a polyatomic molecule to an infrared (IR) laser pulse of varying frequency has been simulated by classical molecular dynamics simulations and by quantum methods based on the path-integral framework (PIMD), as well as quantum thermal baths (QTBs). The outcome of the trajectories was subsequently processed to predict a dissociation spectrum, from the precalculated rate constant. Naphthalene described by a tight-binding potential energy surface was chosen as a testing ground for the present problem, possibly emitting an hydrogen atom after a 12 ps long pulse. At low field intensities, the heating efficiency of the pulse is found to vary similarly as the IR absorption spectrum for all methods considered, reflecting the validity of linear response in this regime. At fields that are sufficiently high to induce statistical dissociation over mass spectrometry timescales, marked differences appear with the spectral features exhibiting additional broadenings and redshift, especially for quantum mechanical descriptions of nuclear motion. Those excessive broadenings are mostly caused by anharmonicities but also convey the inherent approximations of the semiclassical QTB method and point at limitations of the PIMD simulations when used in such strong out-of-equilibrium conditions.

Intramolecular Processes Revealed Using UV-Laser-Induced IR-Fluorescence: A New Perspective on the "Channel Three" of Benzene.

Radiative relaxation in the infrared (IR) is common following nonradiative electronic relaxation processes, but it is rarely measured. We present ultraviolet laser-induced infrared fluorescence (UV-LIIRF) excitation spectroscopy and dispersed UV-LIIRF spectroscopy of gas phase benzene vibronically excited around the onset of channel 3, using a homemade spectrometer. We found that the vibrational IR fluorescence yield is clearly higher when benzene is excited above the onset than when it is excited below. Significant changes in dispersed IR emission profiles resulting from excitations below and above the onset of channel 3 were also observed. These results suggest that isomerization of benzene toward fulvene occurs efficiently below the opening of channel 3 and confirm that channel 3 involves a photophysical relaxation pathway that efficiently competes with isomerization.

Vibron-polaron critical localization in a finite size molecular nanowire.

The small polaron theory is applied to describe the vibron dynamics in an adsorbed nanowire with a special emphasis onto finite size effects. It is shown that the finite size of the nanowire discriminates between side molecules and core molecules which experience a different dressing mechanism. Moreover, the inhomogeneous behavior of the polaron hopping constant is established and it is shown that the core hopping constant depends on the lattice size. However, the property of a lattice with translational invariance is recovered when the size of the nanowire is greater than a critical value. Finally, it is pointed out that these features yield the occurrence of high energy localized states in which both the nature and the number are summarized in a phase diagram in terms of the relevant parameters of the problem (small polaron binding energy, temperature, lattice size).

Direct observation of self-trapped vibrational states in alpha-helices.

Femtosecond infrared pump-probe spectroscopy of the N-H mode of a stable alpha-helix reveals two excited-state absorption bands, which disappear upon unfolding of the helix. A quantitative comparison with polaron theory shows that these two bands reflect two types of two-vibron bound states connected to the trapping of two vibrons at the same site and at nearest neighbor sites, respectively. The latter states originate from an acoustic phonon in the helix, which correlates adjacent sites.

Relaxation channels of two-vibron bound states in alpha-helix proteins.

Relaxation channels for two-vibron bound states in an anharmonic alpha-helix protein are studied. According to a recently established small polaron model [V. Pouthier, Phys. Rev. E 68, 021909 (2003)], it is shown that the relaxation originates in the interaction between the dressed anharmonic vibrons and the remaining phonons. This interaction is responsible for the occurrence of transitions between two-vibron eigenstates mediated by both phonon absorption and phonon emission. At biological temperature, the relaxation rate does not significantly depend on the nature of the two-vibron states involved in the process. The lifetime for both bound and free states is of the same order of magnitude and ranges between 0.1 and 1.0 ps for realistic parameter values. By contrast, the relaxation channels strongly depend on the nature of the two-vibron states which is a consequence of the breatherlike behavior of the two-vibron bound states.

Assessment of an Adult Population's Knowledge Regarding Vaccine-Preventable Diseases.

Background: The purpose of this study was to determine adult patients' knowledge about their history of age-appropriate routine vaccinations and vaccine preventable diseases. Methods: This was a prospective descriptive study using a self-administered questionnaire. During a 9-month period, all patients older than 18 years of age answered a questionnaire at the time of their first visit to a health department travelers' clinic. Questions included knowledge of vaccines that they might have received (against tetanus, diphtheria, polio, measles, rubella, influenza, and pneumococcus); knowledge of illnesses that they might have had (measles and rubella); incidence of visits to a regular physician; and incidence of chronic illness. Results: Two hundred and twenty patients answered the questionnaire. Eighty-two percent had a regular physician whom they had visited within 5 years. Respondents reported their age-appropriate vaccination history as follows: Td-69%; polio-48%; measles-41%; rubella-38%; influenza-68%; and pneumococcal-13%. For any vaccine, approximately one-third of respondents did not know their status. Age, gender, or a regular source of medical care did not influence the results. Conclusions: Adult patients frequently did not receive, or do not know whether they received, recommended immunizations. Until physicians giving primary medical care improve patient education about vaccination status and develop a better system for having patients keep records of their routine vaccinations, travel clinics will have to function, in part, as primary health care providers.

Adverse reactions associated with simultaneous administration of multiple vaccines to travelers.

OBJECTIVE: To determine the frequency of local and systemic adverse reactions following the simultaneous administration of multiple vaccines. DESIGN: Prospective descriptive study using a self-administered questionnaire. All patients seen in a one-year period were given the questionnaire and a stamped, return-addressed envelope to be returned three days after their clinic visits. SETTING: Westchester County (New York) Department of Health Travelers' Clinic. PATIENTS: 984 patients made 1,205 visits. 64% returned the questionnaires. INTERVENTION: The patients reported the occurrence and duration of local and systemic reactions three days after the clinic visit. Demographic data, names of the vaccines, and a description of the injection site of each vaccine were collected separately by clinic staff for each patient at each visit. RESULTS: 58% of the patients reported local reactions and 39.5% at least one systemic complaint. The rate of local reactions increased from 45% with 1 injection in an arm to 78% with > or = 3 (OR = 99). The rate of systemic reactions increased from 25% following the administration of 1 vaccine to 70% with > or = 5 (OR = 7). Number of vaccines did not influence duration or severity of reaction. Age and gender were not associated with frequency of reactions. CONCLUSION: Side effects for vaccination of travelers are common. Increasing the number of vaccines is associated with increasing the rates of local and systemic reactions. These reactions are generally minor and should not be a reason to withhold multiple vaccinations to patients when needed.

Death takes a ride. Alcohol-associated single vehicle fatalities revisited.

Records from the Medical Examiner's Office of Westchester County (1980 population = 866,599) were studied for trends in blood alcohol levels in drivers who died after single vehicle accidents. Findings for all motorists (N = 102) who died in the earliest available eight-year period, 1952-1959, were compared with findings for all motorists (N = 183) who died from 1980 to 1987. The mean age of subjects in the two periods did not differ (37.3 yr +/- 15.4 SD versus 35.4 yr +/- 16.8 SD), and mean blood alcohol levels were nearly identical (0.14% +/- 0.12 SD) versus 0.13% +/- 0.12 SD). Based on the increase in vehicular miles travelled during the two periods, there may have been a 20-25% reduction in alcohol-associated mortality over a 30-year period. Following legislation raising the minimum drinking age to 21, no fatally injured drivers 20 years of age or under have had blood alcohol levels greater than or equal to 0.10%.

Clinical criteria for the detection of pneumonia in adults: guidelines for ordering chest roentgenograms in the emergency department.

Adults presenting to an emergency department with acute respiratory illness were studied prospectively in an effort to identify sensitive clinical criteria for the diagnosis of pneumonia. Of 308 patients studied, 118 (38%) had definite or equivocal infiltrates and were considered to have pneumonia. No single symptom or sign was reliably predictive of pneumonia. Cough was the most common symptom in patients with pneumonia (86%), but was equally common in those with other respiratory illness. Fever was absent in 36 patients with pneumonia (31%). Abnormal findings on lung examination, that is, rales, rhonchi, decreased breath sounds, wheezes, altered fremitus, egophony, and percussion dullness, were each found in fewer than half of the patients with pneumonia. Twenty-six patients (22%) with a completely normal chest examination had pneumonia. Abnormal vital signs (temperature greater than 37.8 degrees C (100 degrees F), pulse greater than 100/min, or respirations greater than 20/min) were 97% sensitive for the detection of pneumonia. These criteria retained their sensitivity when films were subjected to a second, blinded interpretation by a senior radiologist. We conclude that restricting chest roentgenograms to patients with at least one abnormal vital sign will detect almost all radiographically demonstrable pneumonia in adult emergency department patients.

Immunization. A continuing need.

Many vaccines are available to prevent potentially fatal disease. It is especially important for all of us who provide care to review periodically the current recommendations, since they are not static. Changes are based not only on the availability of improved vaccines, but also on knowledge of the diseases and altering societal and epidemiologic circumstances. We owe it to all our patients to be meticulous in maintaining up-to-date immunization records as well as to be knowledgeable about the indications and contraindications for each vaccine. Finally, it is important to remember that the immunization status of adults has been overlooked too often. This is no longer justifiable in light of current knowledge.